This invention is related to co-pending application entitled xe2x80x9cSENSOR AND METHOD FOR SENSING ARTERIAL PULSE PRESSURExe2x80x9d and to co-pending application entitled xe2x80x9cAPPARATUS AND METHOD FOR BLOOD PRESSURE PULSE WAVEFORM CONTOUR ANALYSISxe2x80x9d both filed on even date herewith and incorporated herein by reference.
This invention relates to the field of mechanical positioners, and more specifically to a method and apparatus of holding and positioning an arterial pulse pressure sensor relative to the radial artery of a human wrist.
Conventionally, blood pressure has been measured by one of four basic methods: invasive, oscillometric, auscultatory and tonometric. The invasive method, also known as an arterial-line method (or xe2x80x9cA-linexe2x80x9d), typically involves insertion of a needle or catheter into an artery. A transducer connected by a fluid column to the needle or catheter is used to determine exact arterial pressure. With proper instrumentation, systolic, diastolic, and mean arterial pressures may be determined, and a blood-pressure waveform may be recorded. This invasive method is difficult to set up, is expensive and time consuming, and involves a potential medical risk to the patient. Set up of the arterial-line method poses technical problems. Resonance often occurs and causes significant errors. Also, if a blood clot forms on the end of the needle or catheter, or the end of the needle or catheter is located against an arterial wall, a large error may result. To eliminate or reduce these errors, the setup must be checked, flushed, and adjusted frequently. A skilled medical practitioner is required to insert a needle or catheter into the artery, which contributes to the expense of this method. Medical complications are also possible, such as infection, nerve and/or blood vessel damage.
The other three traditional methods of measuring blood pressure are non-inyasive. The oscillometric method measures the amplitude of blood-pressure oscillations in an inflated cuff. Typically, the cuff is placed around the upper arm of the patient and then pressurized to different levels. Mean pressure is determined by sweeping the cuff pressure and determining the cuff pressure at the instant the peak amplitude occurs. Systolic and diastolic pressure is determined by cuff pressure when the pressure oscillation is at some predetermined ratio of peak amplitude.
The auscultatory method also involves inflation of a cuff placed around the upper arm of the patient. After inflation of the cuff to a point where circulation is stopped, the cuff is permitted to deflate. Systolic pressure is indicated when Korotkoff sounds begin to occur as the cuff is deflated. Diastolic pressure is indicated when the Korotkoff sounds become muffled or disappear.
The fourth method used to determine arterial blood pressure has been tonometry. The tonometric method typically involves a transducer positioned over a superficial artery. The transducer may include an array of pressure-sensitive elements. A hold-down force is applied to the transducer in order to partially flatten the wall of the underlying artery without occluding the artery. Each of the pressure-sensitive elements in the array typically has at least one dimension smaller than the lumen of the underlying artery in which blood pressure is measured. The transducer is positioned such that at least one of the individual pressure sensitive elements is over at least a portion of the underlying artery. The output from one or more of the pressure sensitive elements is selected for monitoring blood pressure. These tonometric systems either use an upper-arm cuff to calibrate blood-pressure values, or they measure a reference pressure directly from the wrist and correlate this with arterial pressure. However, when a patient moves, recalibration of the tonometric system is often required because the system may experience a change in electrical gains. Because the accuracy of such tonometric systems depends upon the accurate positioning of the individual pressure sensitive element over the underlying artery, placement of the transducer is critical. Consequently, placement of the transducer with these tonometric systems is time-consuming and prone to error. Also, expensive electromechanical systems guided by software/hardware computer approaches are often used to assist in maintaining transducer placement.
The oscillometric, auscultatory and tonometric methods measure and detect blood pressure by sensing force or displacement caused by blood-pressure pulses within the underlying artery that is at least partially compressed or flattened. The blood pressure is sensed by measuring forces exerted by blood-pressure pulses in a direction perpendicular to the underlying artery. However, with these methods, the blood-pressure pulse also exerts forces parallel to the underlying artery as the blood-pressure pulses cross the edges of the sensor which is pressed against the skin overlying the underlying artery of the patient. In particular, with the oscillometric and the auscultatory methods, parallel forces are exerted on the edges or sides of the cuff. With the tonometric method, parallel forces are exerted on the edges of the transducer. These parallel forces exerted upon the sensor by the blood-pressure pulses create a pressure gradient across the pressure sensitive elements. This uneven pressure gradient creates at least two different pressures, one pressure at the edge of the pressure sensitive element and a second pressure directly beneath the pressure sensitive element. As a result, the oscillometric, auscultatory and tonometric methods can produce inaccurate and inconsistent blood-pressure measurements.
Further, the oscillometric and auscultatory methods are directed at determining the systolic, diastolic, and/or mean blood-pressure values, but are not suited to providing a calibrated waveform of the arterial pulse pressure.
There is a need to non-invasively obtain an accurate, repeatable blood-pressure waveform from the radial artery.
The present invention provides a method and a sensor holding and positioning device. In one embodiment, the device includes a sensor base having two feet, the base forming a raised bridge between the two feet. The bridge has one or more cross members spanning all or part of the space between the two feet. A sensor suspension including a sensor holder and sensor-height-adjustment mechanism is coupled by a pivot-arm axle to the sensor base, such that the sensor suspension is able to rotate in an arc about the long axis of the axle. In one such embodiment, the device further includes a pressure sensor attached to the sensor holder of the sensor suspension. In another such embodiment the sensor suspension is able to slide back and forth along a line parallel to the long axis of the axle.
In one embodiment, the two feet are each elongate and they are substantially parallel to one another. In one such embodiment, the axle is also coupled to and between the sensor suspension and the sensor base such that the sensor suspension is able to slide back and forth along a line that is parallel to the long axis of the axle and parallel to the two feet. In another such embodiment, the axle is rotatably coupled to the sensor base such that the long axis of the axle can be rotated about a point on the long axis and thus positioned to each of two or more angular positions.
Another aspect of the present invention provides a sensor holding and positioning device that includes a sensor base having two parallel elongate feet, the base forming a bridge between the two feet with the bridge having two cross members spanning all or part of the space between the two feet, each cross member including a through hole that is parallel to the elongate axes of the feet; and a pivot-arm apparatus. The pivot-arm apparatus includes a sensor suspension including a sensor holding member and an axle extending from two opposite sides of the holding member, the axle mounted in the through holes of the cross members to slide and rotate freely in the through holes, whereby the sensor holder may be slid back and forth between the cross members in a line parallel to the elongate feet and rotated about the axis of the axle.
Yet another aspect of the present invention provides a sensor holding and positioning device that includes a sensor bridge apparatus including one or more feet members on each of opposite sides of a bottom of the apparatus and a pair of cross members on opposite ends of the bridge apparatus and elevated above the feet members, the cross members spanning all or part of the space between the opposite sides of the apparatus, a sensor suspension mounted to the cross members, and a sensor holder held by the sensor suspension in a position between the feet of the sensor bridge apparatus. This allows the sensor holder to be positioned above a desired location on a human or animal body.
Still another aspect of the present invention provides a sensor holding and positioning device that includes a sensor bridge base including one or more feet members and one or more support members elevated above the feet members, a sensor suspension mounted to the support members, and a sensor holder held by the sensor suspension in a position beside one or more feet of the sensor bridge base. This allows the sensor holder to be positioned above a desired location on a human or animal body.
In one such embodiment, this device further includes a pressure sensor attached to the sensor holder of the sensor suspension. In another such embodiment, the device further includes an axle having a long axis, the axle coupled to and between the sensor suspension and the sensor bridge base such that the sensor suspension is able to slide back and forth along a line parallel to the long axis of the axle. In one such embodiment, the axle is also coupled to and between the sensor suspension and the sensor base such that the sensor suspension is able to rotate in an arc about the long axis of the axle.
In another such embodiment, the device further includes a pivot-arm axle having a long axis, the axle coupled to and between the sensor suspension and the sensor base such that the sensor suspension is able to rotate in an arc about the long axis of the axle.
In one such embodiment, the one or more feet members include two feet that are each elongate and substantially parallel to one another. In one such embodiment, the device further includes an axle having a long axis, wherein the axle is coupled to and between the sensor suspension and the sensor base such that the sensor suspension is able to slide back and forth along a line that is parallel to the long axis of the axle and parallel to the two feet.
In one such embodiment, the device further includes an axle having a long axis, the axle is coupled to and between the sensor suspension and the sensor base, wherein the axle is rotatably coupled to the sensor base such that the long axis of the axle can be rotated about a point on the long axis and thus positioned to each of two or more angular positions.
Yet another aspect of the present invention is a method for positioning an arterial pulse-pressure sensor over the radial artery. The method includes the steps of: immobilizing the wrist with a wrist stabilizer; providing a sensor holding and positioning device which includes two or more feet allowing the device to be positioned with at least one of the two or more feet on each of opposite sides of the radial artery and a sensor held by the device between the feet; positioning the device with the sensor above the radial artery and at least one of the two or more feet on each side of the radial artery; and applying the sensor against the human patient""s skin overlying the radial artery and urging or pressing the sensor against the radial artery. In one embodiment, the method further includes the step of using a sensor-positioning member included with the device to position an arterial pulse-pressure sensor on top of the radial artery.
Another aspect of the present invention is a pulse-waveform acquisition system. In one embodiment, the system includes a wrist stabilizer, the stabilizer comprising a first member shaped on a forearm portion to conform to contours of a forearm, shaped on a wrist portion to contours of a wrist, and shaped on a proximal hand portion end (an end opposite the forearm portion) to the contours of a hand, and forming an angle of approximately 150 degrees between the forearm portion and the hand portion, the stabilizer further including straps for holding the forearm and and to the stabilizer. In another embodiment, the system also includes a sensor holding and positioning device, the device comprising: a sensor bridge base including one or more feet members and one or more support members elevated above the feet members; a sensor suspension mounted to the support members; and a sensor holder held by the sensor suspension in a position beside one or more feet of the sensor bridge base. In another embodiment, the pulse-waveform acquisition system further includes a pressure sensor attached to the sensor holder of the sensor suspension.